Modern vehicle fuel systems generally include a vapor storage canister to collect vapors from the fuel tank. Typically, a vent line runs from a vapor pressure chamber located at the top of the fuel tank to the storage canister. If, during filling of the tank, liquid is allowed to rise high enough in the tank to enter the vent line, there is the possibility that liquid fuel could contaminate the adsorbent material in the vapor storage canister.
U.S. Pat. No. 4,756,328 to Sherwood, assigned to the assignee of the present invention, protects the canister vent line from liquid fuel in the event of tank overfill or excessive tank tilting through the use of a float ball valve system. This type of valve system prevents further entry of liquid fuel into the tank only after the tank has been filled nearly to the top. Also, the use of a float ball valve system has the potential drawback of the float ball being pushed upward into the closed position by the flow of the fuel vapor. Additionally, since the float ball is very light, gravity does not provide a great deal of force to pull it down off of the vent line opening. Hence, the stickier and more effective sealing surfaces of the vent line opening cannot be used without some additional mechanism to kick the lightweight float ball off of the vent line opening to reopen the valve.
It is known, in general, to construct a shutoff valve by supporting a weight with a spring below the canister vent line. When the vehicle is relatively level, the weight compresses the spring and leaves the vent line open. Should the vehicle tilt sufficiently, the spring can extend enough to push the weight up and close the vent line. A system that could actually prevent fuel tank overfill in the first instance, thereby eliminating the need for a float ball, but that also prohibited liquid fuel entry into the vent line in the event of tank tilting would avoid the potential problems associated with the float ball valve system mentioned above.